Solved Custom SMTP: SSL/TLS vs. STARTTLS

[lesthre]

Hi all,

we experienced an issue while setting up a custom SMTP server a while ago.

For our mail server we use STARTTLS and were not able to get our PBX send emails using our own SMTP.
From the error message, we were able to see that you use MailKit as a backend for mails.

We then did some tests with MailKit compiled locally and were able to reproduce the issue.

The switch in the 3CX admin UI "Enable SSL/TLS " only seems to switch between the options SecureSocketOptions.SslOnConnect and SecureSocketOptions.None in MailKit (just guessing).
With our custom SMTP we would need the option SecureSocketOptions.StartTls.

We worked our way around this by setting up a local mail relay on the PBX server so this is in no way a problem that needs to be adressed right away (or at all).
I just wanted to bring up this issue and ask if you would consider expanding the admin UI a bit in order to switch between all options available in MailKit for setting up a custom SMTP.

Thanks,
lesthre

 

[cobaltit]

Is there a reason you went through all this trouble instead of just using the 3CX SMTP server?

 

[StefanW]

we do support StartSSL, is there any information in the system service log from the PBX which would detail more? To be noted, we expect TLS1.2 on the SMTP server.

 

[lesthre]

Thanks for your answer.

As a matter of fact I just retried using our custom SMTP directly and it worked out of the box.
The last time I tried was back in 2019 and I was just reminded by another forum post that this issue existed.
So probably either something within 3CX or on our SMTP server changed in between.

Anyways, thanks for your answer and please consider this issue as resolved/non-existent.